1. Field of the Invention
This invention relates to magnetic memory devices, and more particularly, to field-inducing line configurations arranged adjacent to magnetic cell junctions.
2. Description of the Related Art
The following descriptions and examples are given as background information only.
Recently, advancements in the use of magneto-resistive materials have progressed the development of magnetic random access memory (MRAM) devices to function as viable non-volatile memory circuits. In general, MRAM circuits exploit the electromagnetic properties of magneto-resistive materials to set and maintain information stored within individual magnetic memory cell junctions of the circuit. In particular, MRAM circuits utilize magnetization direction to store information within a memory cell junction, and differential resistance measurements to read information from the memory cell junction. Typically, an MRAM device includes a plurality of conductive lines with which to generate magnetic fields such that the magnetic direction of one or more memory cell junctions may be changed or oriented. Consequently, the conductive lines may also be referred to as xe2x80x9cfield-inducing lines.xe2x80x9d In some cases, the conductive lines may be referred to as xe2x80x9cbitxe2x80x9d and xe2x80x9cdigitxe2x80x9d lines. Generally, xe2x80x9cbitxe2x80x9d lines may refer to conductive lines arranged in contact with memory cell junctions that are used for both write and read operations of the memory cell junctions. xe2x80x9cDigitxe2x80x9d lines, on the other hand, may refer to conductive lines spaced adjacent to the memory cell junctions that are used primarily during write operations of the memory cell junctions.
Typically, bit lines and digit lines are formed as substantially straight and contiguous structures of metal having uniform widths. In most cases, it is desirable to fabricate a field-inducing line with a relatively low amount of resistivity. As such, bit lines and digit lines typically include a single bulk material such as, aluminum or copper, for example. In some cases, the conductive lines may further include a magnetic cladding layer, such as nickel-iron or cobalt-iron, to concentrate a magnetic field in a particular direction. In general, a xe2x80x9ccladding layer,xe2x80x9d as used herein, may refer to a metal sheathe used to cover or line a portion of a metal structure. Typically, the placement of a cladding layer within a field-inducing line of a magnetic memory cell device may be along the surfaces of the bit lines and/or digit lines farthest away from the magnetic cell junctions of the device. For example, in an embodiment in which a conductive line is arranged above a memory cell junction, a cladding layer may comprise the sidewalls and upper surface of the conductive line. However, in an embodiment in which a conductive line is alternatively or additionally arranged below the memory cell junction, a cladding layer included within such a lower conductive line may comprise the sidewalls and lower surface of the conductive line. In this manner, the magnetic cladding layer included within the bit and/or digit lines of a magnetic memory cell device may advantageously focus a generated magnetic field toward a memory cell junction. As a result, the magnetic direction of the memory cell junction may be more easily oriented.
Unfortunately, in some cases, the combination of an aluminum structure with a cladding layer may prove to be difficult to fabricate. In particular, forming a reliable device with an aluminum field-inducing line having a cladding layer below a memory cell junction is generally very difficult. Typically, an aluminum line is patterned rather than formed by the dual damascene technique. In general, the xe2x80x9cdual damascene techniquexe2x80x9d may refer to a method in which a structure is formed by filling a trench with a material and polishing the material to be coplanar with the upper surface of the trench. Such a fill and polish technique is generally undesirable for fabricating an aluminum structure, since polishing aluminum is difficult and produces many fabrication issues. In particular, aluminum tends to oxidize easily and aluminum oxide is typically difficult to remove during a polishing process. In addition, even in an embodiment in which aluminum oxide can be removed during a polishing process, the underlying aluminum material is generally softer than aluminum oxide. Consequently, in such an embodiment, the polishing process tends to create several other fabrication problems, including but not limited to scratches, dishing, and surface roughness. As such, aluminum lines are generally formed using a patterning process. Such a patterning process, however does not allow a cladding layer to be formed along the bottom and sidewalls of a structure. Therefore, forming a reliable device with an aluminum field-inducing line having a cladding layer below a memory cell junction is generally improbable.
Copper, on the other hand, may be feasibly fabricated using a dual damascene process and therefore, may be fabricated with a cladding layer. However, the use of copper creates a variety of fabrication concerns, including safety hazards, reliability issues, and the possibility of rendering fabrication equipment and/or devices unusable. In particular, copper has a high solubility with silicon and therefore, can readily change the properties of silicon and its function within a device. Such a change in properties can cause a device to malfunction, rendering the device unusable or at least having reduced reliability. The infusion of copper with silicon may originate through the diffusion of ions within structures and layers of the device during or subsequent to the fabrication process of the device. In addition or alternatively, copper and silicon infusion may occur through contamination of the fabrication equipment. Consequently, fabrication equipment contaminated with copper may need to be cleaned and purged before any further fabrication may be conducted to prevent occurrences of infusing copper with silicon. Such a clean-up process can be extensive, requiring large amounts of time and money. As such, in some embodiments, it may be desirable to limit the amount of copper used in the fabrication of semiconductor devices.
Accordingly, it may be advantageous to develop an MRAM device with a different field-inducing line configuration than used in conventional devices. In particular, it may be advantageous to develop a field-inducing line configuration having relatively low resistivity and, in some embodiments, a cladding layer included therein. In addition, it may be advantageous to develop a field-inducing line configuration that is substantially absent of copper.
The problems outlined above may be in large part addressed by a magnetic random access memory (MRAM) device having a different field-inducing line configuration than used in conventional devices. In some cases, the field-inducing line may include a first layer with a plurality of dielectrically spaced conductive segments. In addition, the field-inducing line may include a second layer with a conductive portion in contact with at least two of the plurality of the dielectrically spaced conductive segments of the first layer. In some embodiments, the conductive portion of the second layer may span across and in contact with all of the dielectrically spaced conductive segments of the first layer. Alternatively, the conductive portion of the second layer may be one of a plurality of dielectrically spaced conductive portions arranged in contact with the plurality of conductive segments of the first layer. In such an embodiment, the plurality of conductive segments of the first layer and the plurality of conductive portions of the second layer may be, in some cases, alternately arranged within the field-inducing line. In other cases, the plurality of conductive segments of the first layer and the plurality of conductive portions of the second layer may be arranged in a different manner.
In any embodiment, the second layer may be arranged vertically closer to magnetic junctions of the device than the first layer is arranged to the magnetic junctions. In addition, the second layer may be formed above or below the first layer. In this manner, the field-inducing line may be arranged above or below a magnetic cell junction of the topography. In some cases, a magnetic junction of the topography may be arranged vertically adjacent to the conductive portion of the second layer. Consequently, a device is provided which includes a conductive line with a first lateral portion vertically aligned with a magnetic junction. In some cases, a surface of such a first lateral portion arranged farthest from the magnetic cell junction may include a cladding layer. Alternatively, the surface of the first lateral portion arranged farthest from the magnetic cell junction may be absent of a cladding layer. In some cases, the first lateral portion may include a cladding layer upon a sidewall surface of the first lateral portion. For example, the first lateral portion may include a cladding layer upon all sidewall surfaces of the first lateral portion, in some embodiments. In other cases, however, the first lateral portion may include a cladding layer upon less than all of the sidewall surfaces of the first lateral portion. In either case, the conductive portion of the second layer of the field-inducing line, as described above, may include a cladding layer outlining either the upper or lower surface along with the sidewalls of the conductive portion.
In contrast, the first layer of the field-inducing line may be substantially absent of a cladding layer. As stated above, the first layer of the field-inducing line may include dielectrically spaced conductive segments. In some embodiments, such dielectrically spaced conductive segments may be arranged in substantial alignment with regions of the device laterally adjacent to magnetic cell junctions of the device. As such, a device is provided which includes a conductive line having a second lateral portion aligned with a region of the device arranged between two magnetic junctions. In some embodiments, the conductive portion of the second layer of the field-inducing line may be arranged vertically adjacent to the dielectrically spaced conductive segments of the first layer of the field-inducing line and, therefore, may comprise a part of the second lateral portion. Alternatively, the conductive portion of the second layer of the field-inducing line may not be arranged vertically adjacent to the conductive segments of the first layer and, therefore, may not be part of the second lateral portion. Consequently, the second lateral portion may or may not include a cladding layer. However, in any embodiment, the surface of the second lateral portion arranged farthest from the region of the device arranged between two magnetic junctions may preferably be absent of a cladding layer, since the first layer of the field-inducing line comprises such a second lateral portion and is preferably absent of a cladding layer.
In some embodiments, the field-inducing line may be adapted to induce a higher magnetic field along a magnetic junction than along a region of the device arranged laterally between magnetic junctions. For example, in some embodiments, the first lateral portion of the field-inducing line may be arranged vertically closer to a magnetic junction of the device than the second lateral portion of the field-inducing line is vertically arranged to a region of the device between the magnetic junction and an adjacent magnetic junction. In addition or alternatively, the first lateral portion may be adapted to conduct a higher density of current than the second lateral portion. In such an embodiment, at least one of the conductive segments of the first layer of the field-inducing line may be thicker than the conductive portion of the second layer in some embodiments. In yet other cases, the thickness of one or more of the conductive segments of the first layer may be less than or substantially similar to the thickness of the conductive portion of the second layer.
In general, the dielectrically spaced conductive segments of the first layer and the conductive portion of the second layer may include any metal material. In some embodiments, the conductive segments of the first layer and the conductive portion of the second layer may include the same material. In other embodiments, however, the conductive segments of the first layer and the conductive portion of the second layer may include different materials. For example, in some embodiments, the dielectrically spaced conductive segments of the first layer may include aluminum while the conductive portion of the second layer may include tungsten. Consequently, in some embodiments, the first lateral portion of the conductive line substantially aligned with an overlying magnetic junction may include a different material than the second lateral portion of the conductive line substantially aligned with a spacing arranged adjacent to the magnetic junction. In some embodiments, the second layer may include a material having lower resistivity than a material included in the first layer. In this manner, the second lateral portion of the field-inducing line may include a material having lower resistivity than a material included in the first lateral portion of the field-inducing line. For example, the second lateral portion may include aluminum, while the first lateral portion may include tungsten. In some cases, the second lateral portion of the field-inducing line may further include at least one of the same materials as the first lateral portion of the field-inducing line. For instance, in the aforementioned example, the second lateral portion may further include tungsten, in some cases.
A method for fabricating a magnetic random access memory device is also contemplated herein. In particular, the method may include patterning a first conductive layer to form a lower portion of a field-inducing line and depositing a second conductive layer upon and in contact with at least a part of the lower portion to form an upper portion of the field-inducing line. Subsequently, the method may include forming one or more magnetic junctions in alignment with the upper portion of the field-inducing line. In some cases, the method may include polishing the second conductive layer prior to forming the one or more magnetic junctions. In addition or alternatively, the method may include depositing a dielectric layer above the lower portion of the field-inducing line and etching one or more trenches within the dielectric layer to expose at least a part of the lower portion prior to depositing the second conductive layer. Such a method may further include depositing a cladding layer within the one or more trenches prior to the step of depositing the second conductive layer. In yet other embodiments, the method may not include forming a cladding layer within the one or more trenches. In either case, the step of patterning the first conductive layer may include forming a plurality of separated conductive segments. In such an embodiment, the step of etching the one or more trenches may include etching a plurality of trenches spaced apart from each other and spanned above the plurality of separated conductive segments.
There may be several advantages to forming a magnetic memory device as described herein. In particular, the method described herein may provide a manner in which to form a field-inducing line with a cladding layer below a magnetic junction without having to contend with the fabrication issues related to copper infusion into silicon. In addition, the configuration of the field-inducing line described herein may, in some embodiments, allow a cladding layer to be formed on five walls (i.e., the bottom and four sidewall surfaces) of a portion of the field-inducing line rather than along three walls (i.e., the bottom and two sidewall surfaces) as compared to conventional field-inducing lines. Moreover, the field-inducing line described herein may be configured to allow a magnetic field to be concentrated along an overlying magnetic junction to more easily orient the magnetic direction of the junction. More specifically, the field-inducing line may be configured to have a higher density of current directly below the magnetic junction than in conventional devices, in some embodiments. In this manner, lower amounts of current may be used to orient the magnetic directions of magnetic junctions than in conventional devices, thereby lowering the overall power requirements of the device described herein. Furthermore, the structure described herein may offer a smooth surface with low resistance. In some embodiments, the field-inducing line described herein may be further used to modulate the temperature of the magnetic cell junction by using the portion of the field-inducing line directly below the magnetic cell junction as a heating element.